Adherence of bacteria to specific target tissues in the host is an important aspect of the pathogenesis of a variety of infectious diseases. In this study we will analyze some factors which enable enterotoxigenic Escherchia coli to colonize the proximal small intestine of animals and man. This colonization is mediated by proteinaceous surface antigens. Several of these antigens have been identified; K88, K99, CFAI and CFAII. Each antigen promotes colonization of a particular species; K88, pigs and occasionally calves; K99 calves and lambs; CFAI and CFAII, humans. The genetic determinants for synthesis of these antigens are located on plasmids. We will study the plasmids which encode these colonization antigens and identify and characterize the specific genes and gene products involved in expression of the antigens. The K88 antigen determinants have been isolated and studied in some detail. In this research we will use recombinant DNA and sequencing techniques to analyze the plasmid and host factors involved in regulation of expression of K88. Plasmid sequences required for the expression of the CFAI and CFAII antigens from human enterotoxigenic strains will be identified and isolated by molecular cloning. The organization of the genes involved in expression of CFAI and CFAII will be determined and the protein products will be identified and characterized in E. coli minicells. DNA-DNA hybridization studies will be used to assess the degree of sequence homology among antigenically distinct colonization factors. Determinants which show a high degree of homology will be further analyzed by DNA sequence analysis. We will also use DNA hybridization to determine whether genetically related factors are present in enterotoxigenic strains from humans and animals which do not express one of the well defined colonization factors. It is anticipated that this research will lead to a better understanding of the factors involved in bacterial adherence and tissue specificity and will contribute to the development of effective programs of prophylaxis and treatment of infectious disease.